The proposed invention is directed to a method and a system for industrial separation of carbon dioxide (CO2) from flue gas, natural gas, syngas or other gas streams mainly containing nitrogen, oxygen, hydrogen, carbon monoxide or methane, where liquid ammonia (NH3) solutions are used as a solvent. The CO2 is absorbed in the solvent in an absorption process. This process may be generally referred to as the CO2 absorption process.
After absorption of the CO2 from a gas with ammonia based solutions, residual ammonia is often still present in the treated gas. This residual ammonia has to be removed in a separate process step, before the treated gas can be further processed or sent to the atmosphere.
Ammonia is removed from the gas in a wash step by scrubbing the flue gas with a wash liquid in an adequate contacting device. This process may be generally referred to as the NH3 absorption process. In general, fresh water or water or weak ammonia solution coming from a stripping process is used as the wash liquid.
After the wash step, the wash liquid will contain the ammonia absorbed from the gas. The wash liquid is then sent to an ammonia stripping process, where the ammonia is separated from the wash liquid. The stripped wash liquid is generally recycled to the wash step. The ammonia separated from the wash liquid leaves the stripping process as a stripper offgas stream containing mainly ammonia, CO2 and water vapor, but also a usually small fraction of non condensable co-absorbed gas components from the flue gas.
The stripper offgas stream is generally either discharged to the atmosphere or introduced into a regenerator unit in which CO2 is separated and removed from the ammonia based solution, and the ammonia based solution depleted of CO2 is recycled to the CO2 absorption.